During combustion, an internal combustion engine oxidizes gasoline and combines hydrogen (H2) and carbon (C) with air. Combustion creates chemical compounds such as carbon dioxide (CO2), water (H2O), carbon monoxide (CO), nitrogen oxides (NOx), unburned hydrocarbons (HC), sulfur oxides (SOx), and other compounds. During an initial startup period after a long soak, the engine is still “cold” after starting and combustion of the gasoline is incomplete. A catalytic converter treats exhaust gases from the engine. During the startup period, the catalytic converter is also “cold” and does not operate optimally.
Besides fuel vaporization and combustion challenges during cold start, the level and variability of electrical loads make cold start fuel and spark control difficult. As a result, a non-optimum cold start fuel calibration is provided that accommodates extreme engine load conditions. In effect, the emissions calibration is penalized for a relatively small percentage of worst-case combinations of ambient temperature, fuel volatility and engine load conditions during cold start.